Mitochondrial protease AtFtsH4 protects ageing Arabidopsis rosettes against oxidative damage under short-day photoperiod

Abstract

Mitochondrial AtFtsH4 protease, whose catalytic site is exposed to the intermembrane space, is one of four inner membrane-bound FtsH proteases in Arabidopsis. We found that the loss of AtFtsH4 altered Arabidopsis leaf morphology at the late stage of rosette growth under short-day photoperiod, while such changes were not observed in ftsh4 mutants grown under long days. These morphological changes were correlated with elevated levels of both reactive oxygen species (ROS) and carbonylated proteins, which strongly suggested that ageing ftsh4 plants experienced oxidative stress. This view was supported by the accumulation of electron-dense material, presumably containing aggregated oxidized proteins, in mitochondria of ftsh4 plants with the most strongly malformed leaf blades. Taken together, our data published in the May issue of Plant J ¹ suggest a link between the lack of AtFtsH4 protease, oxidative stress and altered leaf morphology at the late rosette stage under short days. Here, we present evidence that the onset of altered leaf morphology in ftsh4 correlates with an increase in the abundance of AtFtsH4 transcript observed in wild-type Arabidopsis growing under the same conditions. We also discuss how the lack of AtFtsH4 may cause oxidative stress towards the end of the vegetative growth in short days.

Acknowledgement

This research was supported by a grant from the Ministry of Education and Science, Poland (grant number N N303 3504 33) to H.J.

Figures and Tables

Figure 1 Time-course of AtFtsH4 transcript level detected by quantitative PCR in wild-type plants under long (LD) and short (SD) day conditions. At the early growth stage the transcript level was measured in cotyledons or two-leaved seedlings. Later, between the fourth leaf stage and inflorescence emergence (Inf.emerg.) the youngest leaf was always sampled. In the generative phase, cauline leaves, buds, open flowers and siliques were tested. The arrow indicates the time when subtle leaf malformations become visible in the ftsh4 mutant. Error bars indicate SE.

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